Resonator chamber silencer for gas turbine

ABSTRACT

A gas turbine exhaust silencer for attenuating both highfrequency and low-frequency noises. In the low-frequency silencing section there is a row of acoustically absorbent boxes which are spaced apart to form gas passageways between adjacent opposite sidewalls. Some low-frequency noise is absorbed into the acoustic boxes through perforations in the sidewalls. Aligned with the acoustic boxes, there is a row of hollow, spaced apart, resonator boxes contiguous with the acoustic boxes to continue the gas passageways. Additional low-frequency sound attenuation is provided by the resonator boxes wherein adjacent opposite sidewalls defining the gas passageways have a plurality of openings therein through which sound waves may pass to be reflected off interior walls of the resonator to cancel incoming sound waves.

United States Patent I [191 Lawyer et al. 51 Jan. 9, 1973 [54] RESONATOR CHAMBER SILENCER FOREIGN PATENTS OR APPLICATIONS S TURBINE I 638,407 6/1950 Great Britain ..18l/33 HB [75] Inventors: John F. Lawyer, Albany; David K.

Prugger, Rexfo'rd, both of N.Y. Primary Examiner-Robert S. Ward, Jr. [73] Assignee: General Electric Company Anorfi'ey wmlam crutch et [22] Filed: Oct. 6, 1971 [57] ABSTRACT [21] Appl. No.: 187,090 A gas turbine exhaust silencer for attenuating both high-frequency and low-frequency noises. In the low- 7 frequency silencing section there is a row of acousti- [52] 181/50 0 cally absorbent boxes which are Spaced apart to form [5,11 ,,:-;:---,n 6, B041 2 F0111 iiing izi iizfiii ii 125 i: $5332; ii ti i i e 5 new Search "181/33 33 acoustic boxes through perforations in the sidewalls.

' 181/33 33 33 50,46 Aligned with the acoustic boxes, there is a row of hollow, spaced apart, resonator boxes contiguous with I the acoustic boxes to continue the gas passageways. [56] Rekrences Cited Additional low-frequency sound attenuation is pro- UNITEDSTATES PATENTS vided by the resonator boxes wherein adjacent opposite sidewalls defining the gas passageways have a 2,324,706 1 4943 Jacobson ..l8l/33 l-lB plurality of openings therein through which sound 2,842,222 7/1958 waves may pass to be reflected off interior walls of the I? resonator to cancel incoming sound waves. 3:347:338 10/1967 Childress....-., ..l8l/33 l-lB 7 Claims, 2 Drawing Figures EXHAUST 29 29 PARALLEL T BAFFLE SECTION i= 2' I ill I :E' l [II m \y\ EXPANSION lillill llll |i l T I g j- -y ACOUSTIC lL-ii Lil "Ell "Ell Alli R 2 V 'H\\, x "17 RESONATOR SECTION A c A i i so ciioN IE a lb" 2i ,L raih iii ii 3 I IE EXHAUST 27 PLENUM TURBINE ENCLOSURE r PATENTEI] JAN 9 I975 SHEET 2 OF 2 RESONATOR CHAMBER SILENCER FOR GAS TURBINE BACKGROUND OF THE INVENTION This invention relates, in general, to a gas turbine exhaust silencer for attenuating both high-frequency and low-frequency noises and in particular relates to a gas turbine exhaust silencer with additional low-frequency noise attenuating capacity while minimizing the pres- I sure drop in the exhaust gas flow path.

Technology relating to gas turbine exhaust silencing has largely been directed toward attenuating highfrequency noises. This has resulted in the use of relatively thin, acoustically absorbent parallel baffles a number of which usually span the hot exhaust stack. However, very little effort has been directed towards the silencing of low-frequency exhaust noise emissions.

One effort, which has been directed towards the silencing of both high-frequency and low-frequency exhaust noises, has been put forth in US. Pat. application Ser. No. 181,002 filedon Sept. 16, 1971 in the names of Smith and Frederick for a Gas Turbine Exhaust Silencer and Support and assigned to the assignee of the present invention.

According to that application, a free-standing structural frame is positioned adjacent the exhaust end of a gas turbine. Provided within the frame are two lowfrequency silencing sections and a high-frequency silencing section. Each low-frequency silencing section includes a row of large, acoustically absorbent boxes followed by an expansion section. The high-frequency section comprises a number of parallel baffles which are relatively thin and acoustically absorbent in a higher frequency range. The acoustically absorbent box sections each support an expansion section and in one embodiment the acoustically absorbent box section supports both an expansion section and a parallel baffle section. The acoustically absorbent box sections and the parallel baffle section all attenuate sound by absorbing the sound into an acoustical fill within the respective sections. The expansion sections are merely large enclosed volumes insulated on interior walls which attenuate noise as a result of decreases in gas energy due to decreases in gas pressure.

While the above invention represents a satisfactory working arrangement, it is also well known that decreases in gas pressures in a gas exhaust flow path may result in the building of back pressures which may adversely affect gas turbine efficiencies. Further, it may well be desirable to impart a tuning capability to the low-frequency silencing section so that additional silencing effort may be directed toward critical noise frequencies.

OBJECTS OF THE INVENTION Accordingly, it is one object of the present invention to provide an improved gas turbine exhaust silencer which will attenuate both high-frequency and lowfrequency noises.

Another object of this invention is to provide a gas turbine exhaust silencer which will minimize pressure losses in the hot exhaust gas flow path. I

Still another object of this invention is to provide a gas turbine exhaust silencer which may be tuned" to increase the attenuation of certain noise frequencies.

SUMMARY OF THE INVENTION In a gas turbine exhaust silencer, a low-frequency silencing section comprises a row of spaced apart, acoustically absorbent boxes having opposite adjacent sidewalls which define a plurality of hot gas passageways; and, a contiguous row of spaced apart, hollow resonator boxes which are aligned with the acoustically absorbent boxes so as to continue the hot 0 gas passageways. The spaced apart resonator boxes have adjacent opposite sidewalls, which include a plurality of openings therein, bounding and defining the hot gas passageways so that sound waves pass into the resonator boxes whereupon they are reflected off the interior walls to cancel incoming sound waves. Noise is selectively attenuated through this wave cancellation process while gas pressure losses are minimized throughout the gas passageways.

. Other objects, advantages and features of the present invention will become apparent from the following detailed description of an embodiment thereof taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway isometric view of one embodiment of a gas turbine exhaust silencer.

FIG. 2 is an isometric view of the present invention incorporated into a partial showing of one embodiment of a low-frequency silencing section.

DETAILED DESCRIPTION OF THE INVENTION A gas turbine exhaust silencer, shown in FIG. I, is indicated generally at 11, adjacent the exhaust end of a gas turbine (not shown) housed in a turbine enclosure. The exhaust silencer communicates with the gas turbine through an exhaust plenum and an exhaust transition.

As described in detail in the Smith and Frederick application, the exhaust silencer may be supported by a skeletal structural frame 13 defining an exhaust duct including flanged beams 21 supported by flanged columns 27. This is one embodiment into which the present invention may find application, and, it should be recognized that there may be many other embodiments in which the present invention may be applicable.

In one embodiment of the present invention, there are two low-frequency silencing sections. One of these low-frequency sections includes an acoustic box section and a resonator section. The acoustic box section may comprise a row of conventionally mounted, soundabsorbing boxes or may be similar to the acceleration section" in the Smith and Frederick application. The latter arrangement provides a row of large hollow boxes 35, filled with suitable acoustic thermal insulating material 47 and has a hollow box beam 45 running therethrough for support and ventilation purposes. The box beam, through the acoustic box, rests freely on opposite support beams which define the exhaust duct.

As is shown in FIG. 2, the acoustic boxes are arranged in a row, side by side, and have perforated op-' posite adjacent sidewalls 49 forming a plurality of gas flow passageways 39. Sound is absorbed into the suitable acoustical, thermal insulation 47, which may be fiberglass, through the perforated opposite, adjacent sidewalls. Other closure portions 51, of the acoustic boxes are generally fabricated from non-perforated.

sheet metal.

A resonator section, which forms the subject matter of the present invention, may be supported by the acoustic box section in the manner described in the Smith and Frederick application for an expansion section. The resonator section includes a row of side-byside hollow resonator boxes 69 disposed across the exhaust duct defined by the structural frame and spaced apart so as to be in alignment with the gas passageways 39 formed by opposite, adjacent acoustic box sidewalls 49 and therefore effectively continuing the gas passageways. The resonator boxes 69 have opposite, adjacent sheet metal sidewalls 71 continuing the gas passageways. These sidewalls have a plurality of openings 75 formed therein communicating with the gas passageways 39. Because the gas passageways 39 are continued through the resonator section having the same cross-section area, there is no substantial reduction in exhaust gas velocity and pressure and therefore no back pressure buildup. End walls 79 of the resonator boxes, as distinguished from opposite adjacent sidewalls, are fabricated from non-perforated sheet metal to complete the enclosure.

The resonator boxes may be tuned for different noise attenuations by varying the diameters of the sidewall openings, the center-to-center spacing of the openings and the length and number of resonators in the flow direction.

For example, using one resonator, 4 feet long in the gas flow direction, will result in a certain maximum noise attenuation peak for the silencer (about 60db). If the openings are r-inch diameter on 5% inch centers, the maximum attenuation peak will occur in that third octave band having 100 cycles per second as its center frequency. if the openings are l-inch diameter on 9- inch centers, then, the maximum attenuation peak will occur in the third octave band having 80 cycles per second as its center frequency.

If two resonators are mounted in series, the first resonator being 2 feet long in the gas flow direction having l-inch diameter openings on 9-inch centers, the second also being 2 feet long but having %-inch diameter openings on 5% inch centers, then a broader,

slightly lower (58db) maximum attenuation is attained for the silencer which remains at peak value over the range of frequencies comprising the 80 and l00 cycles per second third octave bands.

Above the resonator section there may be another low-frequency silencing section of the kind disclosed in the Smith and Frederick application. There is self-supporting, upper acoustic box section, aligned with the gas passageways 39 of the first-mentioned acoustic box sectionand the resonator section. Therefore, the gas passageways are further continued, having a substantially constant cross-sectional flowv area thereby minimizing pressure losses. Above the upper acoustic box section, and supported thereby, there may be another resonator section or, as shown in the preferred embodiment, anexpansion section. As was previously mentioned, the expansion section is a large vacant volume in which gas is allowed to decrease in pressure and velocity with a corresponding decrease in sound energy.

Lastly, in the preferred embodiment, a parallel baffle section is supported above the upper acoustic box section and the expansion section. The parallel baffle sec tion includes a row of spaced apart, relatively thin in a direction perpendicular to the gas flow, acoustically absorbent parallel baffles 29. Because of the thin baffle dimensions, they are useful in attenuating highfrequency noise. From the parallel baffle section the hot gases may be exhausted to the atmosphere.

,, OPERATION Hot exhaust gases from the exhaust end of a gas turbine pass through the exhaust plenum and the exhaust transition into an acoustic box section. The row of spaced apart acoustic boxes provide gas passageways through the acoustic box section. Perforated, opposite adjacent sidewalls of the acoustic boxes which defme the gas passageways permit low-frequency sound absorption into the acoustical and thermally insulated boxes.

The hot gases then flow into the resonator section which comprises a row of hollow spaced apart boxes aligned with the acoustic boxes so as to continue the gas passageways. Opposite adjacent resonator box sidewalls .having openings therein permit selected sound wave frequencies to enter the resonator box; be reflected off interior portions of the box and thereafter to cancel incoming sound waves.

Both the acoustic box section and the resonator section are useful in attenuating low-frequency sounds because of their rather broad geometry in a direction perpendicular to the gas flow. Also, the-resonator section may be tuned to attenuate selected low-frequency noises.

The'acoustic box section and the resonator section may be followed by another low-frequency section comprising the same elements or, in the alternative, a low-frequency silencing section comprising an acoustic box section and a hollow expansion section. This other low-frequency section may be entirely eliminated according to silencing needs and only a parallel baffle section may be included following any arrangement of low-frequency silencing sections.

While there is shown what is considered to be, at present, the preferred embodiment of the invention, it is, of course, understood that various other modifications may be made therein. Other modifications may include using the resonator section in a more conventional construction of a gas turbine exhaust silencer. It

is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a gas turbine exhaust silencer having means defining an exhaust duct for carrying exhaust gases to the atmosphere, the combination of: i

a row of acoustically absorbent boxes, disposed across said duct and filled with acoustical, thermal insulating material, said acoustically absorbent boxes being spaced apart to form a plurality of gas passageways in the duct; and,

at least .one contiguous row of substantially empty boxes having hollow interiors and having adjacent opposite sidewalls aligned with said acoustically absorbent boxes to continue the gas passageways;

said adjacent opposite sidewalls formed with openings communicating the gas passageways with the interior of each box.

2. The gas turbineexhaust silencer as recited in claim 1 wherein the means defining an exhaust duct includes a free-standing, self-supporting structural frame.

3. The gas turbine exhaust silencer as recited in claim 1 wherein the size and centerline spacing of the openings may be varied.

4. The gas turbine exhaust silencer as recited in claim 1 wherein the length and number of empty boxes in the direction of the gas flow may be varied.

5. The gas turbine exhaust silencer as recited in claim l wherein there is a second row of acoustically absorbent boxes contiguous with said row of substantially empty boxes and aligned therewith to further continue the gas passageways, and, an expansion section defined by a large vacant chamber contiguous with said second row of acoustically absorbent boxes and disposed within the exhaust duct.

6. The gas turbine exhaust silencer as recited in claim 5 wherein there are a plurality of relativelythin, acoustically absorbent, parallel baffles contiguous with said expansion chamber and disposed across said exhaust duct.

7. In a gas turbine exhaust silencer including a structural frame defining an exhaust duct for carrying exhaust gases to the atmosphere, the combination of:

a first low-frequency silencing section disposed across said duct including a row of acoustically absorbent boxes spaced apart to provide gas passageways, and, at least one contiguous row of resonator boxes aligned with the acoustically absorbent boxes to continue the gas passageways;

a second low-frequency silencing section disposed across said duct including a second row of acoustically absorbent boxes spaced apart to further continue the gas passageways and, an expansion section defined by a large vacant chamber contiguous with said second row of acoustically absorbent boxes and disposed within the exhaust duct; and,

a high-frequency silencing section including a row of relatively thin, acoustically absorbent parallel baffles contiguous with said expansion section and disposed across said exhaust duct. 

1. In a gas turbine exhaust silencer having means defining an exhaust duct for carrying exhaust gases to the atmosphere, the combination of: a row of acoustically absorbent boxes, disposed across said duct and filled with acoustical, thermal insulating material, said acoustically absorbent boxes being spaced apart to form a plurality of gas passageways in the duct; and, at least one contiguous row of substantially empty boxes having hollow interiors and having adjacent opposite sidewalls aligned with said acoustically absorbent boxes to continue the gas passageways; said adjacent opposite sidewalls formed with openings communicating the gas passageways with the interior of each box.
 2. The gas turbine exhaust silencer as recited in claim 1 wherein the means defining an exhaust duct includes a free-standing, self-supporting structural frame.
 3. The gas turbine exhaust silencer as recited in claim 1 wherein the size and centerline spacing of the openings may be varied.
 4. The gas turbine exhaust silencer as recited in claim 1 wherein the length and number of empty boxes in the direction of the gas flow may be varied.
 5. The gas turbine exhaust silencer as recited in claim 1 wherein there is a second row of acoustically absorbent boxes contiguous with said row of substantially empty boxes and aligned therewith to further continue the gas passageways, and, an expansion section defined by a large vacant chamber contiguous with said second row of acoustically absorbent boxes and disposed within the exhaust duct.
 6. The gas turbine exhaust silencer as recited in claim 5 wherein there are a plurality of relatively thin, acoustically absorbent, parallel baffles contiguous with said expansion chamber and disposed across said exhaust duct.
 7. In a gas turbine exhaust silencer including a structural frame defining an exhaust duct for carrying exhaust gases to the atmosphere, the combination of: a first low-frequency silencing section disposed across said duct including a row of acoustically absorbent boxes spaced apart to provide gas passageways, and, at least one contiguous row of resonator boxes aligned with the acoustically absorbent boxes to continue the gas passageways; a second low-frequency silencing section disposed across said duct including a second row of acousTically absorbent boxes spaced apart to further continue the gas passageways and, an expansion section defined by a large vacant chamber contiguous with said second row of acoustically absorbent boxes and disposed within the exhaust duct; and, a high-frequency silencing section including a row of relatively thin, acoustically absorbent parallel baffles contiguous with said expansion section and disposed across said exhaust duct. 